f  U  I   /  JNIVfcJISiTY  Of  CALIFOWtH 

f    ■  LIEF 

UNIVERSITY  OF  CALIFORNIA  PUBLICATIONS    COuE8E  I*' M^CULTUKt 


COPY  2 


} 


COLLEGE  OF  AGRICULTURE 

AGRICULTURAL  EXPERIMENT  STATION 

BERKELEY.  CALIFORNIA 


GRAPE  VINEGAR 


BY 

FREDERIC  T.  BIOLETTI 


BULLETIN  No.  227 


SACRAMENTO 
Friend  Wm.  Richardson       -      -      Superintendent  of  State  Printing 

1912 


Benjamin  Ide  Wheeler,  President  of  the  University. 

EXPERIMENT  STATION  STAFF. 

B.  J.  Wickson,  M.A.,  Director  and  Horticulturist. 
E.  W.   Hilgard,  Ph.D.,  LL.D.,   Chemist    (Emeritus). 
W.  A.  Setchell,  Ph.D.,  Botanist. 

Leroy  Anderson,  Ph.D.,  Dairy  Industry  and  Superintendent  University  Farm  Schools. 

M.   E.   Jaffa,  M.S.,   Nutrition  Expert. 

P.  H.  Loughridge,  Ph.D.,  Soil  Chemist  and  Physicist  (Emeritus). 

C.  W.  Woodworth,  M.S.,   Entomologist. 

Ralph  E.  Smith,  B.S.,   Plant  Pathologist  and  Superintendent  of  Southern  California 

Pathological    Laboratory   and   Experiment    Station. 
G.  W.  Shaw,  M.A.,  Ph.D.,  Experimental  Agronomist  and  Agricultural  Technologist,  in 

charge  of  Cereal  Stations. 

E.  W.  Major,  B.Agr.,  Animal. Industry. 

B.  A.   Etcheverry,  B.S.,   Irrigation   Expert. 

F.  T.  Bioletti,  M.S.,  Viticulturist. 

W.  T.  Clarke,  B.S.,  Assistant  Horticulturist  and  Superintendent  of  University  Exten- 
sion  in   Agriculture. 

John  S.  Burd,  B.S.,  Chemist,  in  charge  of  Fertilizer  Control. 

J.  E.  Coit,  Ph.D.,  Assistant  Pomologist,  Riverside. 

George  E.  Colby,  M.S.,  Chemist  (Fruits,  Waters,  and  Insecticides),  in  charge  of 
Chemical   Laboratory. 

H.  J.  Quayle,  M.S.,  Assistant  Entomologist. 

K.  M.  Hall,  Ph.D.,  Assistant  Botanist. 

C.  M.  Haring,  D.V.M.,  Assistant  Veterinarian  and  Bacteriologist. 
E.  B.  Babcock,  B.S.,  Assistant  Agricultural  Education. 

W.  B.  Herms,  M.A.,  Assistant  Entomologist. 

W.  T.  Horne,  B.S.,  Assistant  Plant  Pathologist. 

C.  B.  Lipman,  Ph.D.,  Soil  Chemist  and  Bacteriologist. 

A.  J.  Gaumnitz,  Assistant  Agronomist,  University  Farm,  Davis. 
N.  D.  Ingham,  B.S.,  Assistant  in  Sylviculture,  Santa  Monica. 
T.  F.  Hunt,  B.S.,  Assistant  Plant  Pathologist. 

P.  L.  McCreary,  B.S.,  Chemist  in  Fertilizer  Control. 

E.  H.  Hagemann,  Assistant  in  Dairying,  Davis. 

R.  M.  Roberts,  Farm  Manager,  University  Farm,  Davis. 

B.  S.  Brown,  B.S.A.,  Assistant  Horticulturist,  University  Farm,  Davis. 
J.  I.  Thompson,  B.S.,  Assistant  Animal  Industry,  Davis. 

J.  C.  Bridwell,  B.S.,  Assistant  Entomologist. 
L.  Bonnet,  I. A.,  Assistant  Viticulturist. 

F.  C.  H.  Flossfeder,  Assistant  in  Viticulture,  University  Farm,  Davis. 
P.  L.  Hibbard,  B.S.,  Assistant  Fertilizer  Control  Laboratory. 

C  H.  McCharles,  M.S.,  Assistant  Agricultural  Chemical  Laboratory. 

B.  A.  Madson,  B.S.A.,  Assistant  Experimental  Agronomist. 
Howard  Phillips,  B.S.,  Assistant  Animal  Industry,  Davis. 

Walter  E.   Packard,  M.S.,  Field  Assistant  Imperial  Valley  Investigation,  El  Centre 
L.  M.  Davis,  B.S.,  Assistant  in  Dairy  Husbandry,  University  Farm,  Davis. 
S.  S.  Rogers,  B.S.,  Assistant  Plant  Pathologist,  Plant  Disease  Laboratory,  Whittier. 
H.  A.  Ruehe,  B.S.A.,  Assistant  in  Dairy  Husbandry,  University  Farm,  Davis. 

C.  O.  Smith,  M.S.,  Assistant  Plant  Pathologist,  Plant  Disease  Laboratory,  Whittier. 

E.  H.  Smith,  M.S.,  Assistant  Plant  Pathologist. 

C    L.  Roadhouse,  D.V.M.,  Assistant  in  Veterinary  Science. 

F.  M.   Hayes,  D.V.M.,  Assistant  Veterinarian. 

M.  E.  Stover,  B.S.,  Assistant  in  Agricultural  Chemical  Laboratory. 

W.  H.  Volck,  Field  Assistant  in  Entomology,  Watsonville. 

E.  L.  Morris,  Field  Assistant  in  Entomology,  San  Jose. 

E.  E.  Thomas,  B.S.,  Assistant  Chemist,  Plant  Disease  Laboratory,  Whittier. 

A.  B.  Shaw,  B.S.,  Assistant  in  Entomology. 

G.  P.  Gray,  M.S.,  Chemist  in  Insecticides. 

H.   D.   Young,    B.S.,   Assistant   in  Agricultural   Chemistry,    Plant   Disease   Laboratory, 

Whittier. 
A.  R.  Tylor,  B.S.,  Assistant  in  Plant  Pathology,  Plant  Disease  Laboratory,  Whittier. 
E.  W.  Rust,  A.B.,  Assistant  in  Entomology,  Plant  Disease  Laboratory,  Whittier. 
L.  T.   Sharp,  B.S.,  Assistant  in  Soils. 
W.  V.  Cruess,  B.S.,  Assistant  in  Zymology. 
J.  F.  Mitchell,  D.V.M.,  Assistant  in  Veterinary  Laboratory. 
W.  B.  Boys,  B.S.,  Assistant  Cerealist. 
M.  E.  Holter,  B.S.,  Assistant  Soil  Chemist. 

Anna  M.  Lute,  A.B.,  Scientific  Assistant,  U.  S.  Dept.  of  Agriculture. 
J.  C.  Roper,  Patron,  University  Forestry  Station,  Chico. 
E.  C.  Miller,  Foreman,  Forestry  Station,  Chico. 

D.  L.  Bunnell,  Secretary  to  Director. 


CONTENTS. 


Page. 

I.     Introduction    341 

II.     Definitions   and    Standards 341 

III.  Classes  of  Vinegar:  Raw  Material 343 

IV.  Wine   Vinegar   343 

V.     Alcoholic  Fermentation   344 

VI.     Acetic    Fermentation    347 

VII.     Yield   of   Vinegar 349 

VIII.     Processes  of  Manufacture 350 

a.  Domestic   Methods    351 

b.  Industrial    Methods    352 

c.  Rapid  or  German  Process 354 

IX.     After  Treatment  356 

a.  Clearing    356 

b.  Decoloration    356 

c.  Pasteurizing    356 

d.  Aging    357 

e.  Fining,   filtering,  bottling   357 

X.     Diseases    357 

a.  Secondary  Fermentations 357 

b.  Blackening    359 

c.  Animal    parasites    359 

XI.     Outline  of  the  Operations  of  Vinegar  Making 360 

a.  Gathering  the  Grapes 360 

b.  Crushing    360 

c.  Extraction  of  the  Juice 360 

d.  Alcoholic    Fermentation    361 

e.  Treatment  of  the   Wine 361 

f.  Acetic   Fermentation    361 

g.  After   Treatment  and  Aging 362 

h.     Preparation  for  Sale 362 

XII.     Tests  of  Use  to  Vinegar  Makers 362 

a.  Sugar    363 

b.  Alcohol    364 

c.  Acid    365 


Digitized  by  the  Internet  Archive 

in  2012  with  funding  from 

University  of  California,  Davis  Libraries 


http://www.archive.org/details/grapevinegar227biol 


GRAPE  VINEGAR. 


I.     INTRODUCTION. 

With  the  ever  increasing  extension  of  the  grape-growing  industry 
in  California  it  is  desirable  that  every  possible  profitable  outlet  for 
the  crops  should  be  utilized.  One  important  outlet  which  at  present 
is  but  incompletely  utilized  is  the  manufacture  of  high  class  vinegar. 

Many  grapes  which  are  unsuitable  for  drying,  shipping,  or  wine- 
making  can  be  turned  into  excellent  vinegar.  Vinegar  of  high  quality 
is  in  fact  so  rare  and  so  difficult  to  procure  that  this  may  be  the  most 
profitable  use,  in  some  cases,  to  which  even  the  best  grapes  can  be  put. 
Wine  vinegar,  however,  can  not,  even  under  the  most  favorable  condi- 
tions, compete  in  cheapness  with  vinegar  made  from  distilled  alcohol 
or  the  numerous  waste  products  which  at  present  are  the  source  of  the 
main  bulk  of  the  vinegar  found  in  commerce.  Good  wine  vinegar  is 
as  costly  to  make  as  good  wine  and  more  costly  than  poor.  It  can  be 
sold  at  a  profit,  therefore,  only  at  a  price  comparable  with  that  of  good 
wine,  which  is  considerably  higher  than  that  of  ordinary  vinegar. 

If  wine  vinegar  is  to  be  produced  at  a  profit,  it  must  be  made  intelli- 
gently and  in  such  a  manner  as  to  produce  and  preserve  those  quali- 
ties to  which  it  owes  its  reputation  for  superiority  over  all  other  classes 
of  vinegar. 

Good  vinegar  can  not  be  made  from  moldy  grapes  or  spoiled  wine 
and  its  manufacture  requires  as  much  knowledge  and  care  as  that  of 
good  wine.  Unlike  the  latter,  however,  it  can  be  successfully  produced 
on  a  small  scale  for  domestic  purposes.  With  a  few  boxes  of  good 
grapes  and  some  small  casks,  vinegar  of  the  best  quality  can  be  made 
for  home  use,  far  superior  in  wholesomeness  and  palatability  to  any 
that  can  be  bought  in  the  general  market  without  paying  extravagant 
prices.  To  serve  as  an  outlet  for  any  considerable  portion  of  the  grape 
crop,  however,  vinegar  must  be  made  on  an  industrial  scale. 

In  the  open  market,  wine  vinegar  can  compete  with  other  vinegars 
only  on  the  score  of  quality.  To  attain  this  quality  the  best  methods 
of  vinegar  making  must  be  understood  and  intelligently  applied. 

II.     DEFINITIONS    AND    STANDARDS. 

Vinegar  has  been  defined  as :  "A  condiment  made  from  various  sugary 
or  starchy  substances  by  alcoholic  and  subsequent  acetic  fermentation. ' ' 
It  is  defined  more  fully  by  the  United  States  "Standards  of  purity  for 
Food  Products, ' '  as  follows  : 

1.  Vinegar,  cider  vinegar,  apple  vinegar,  is  the  product  made  by 
the  alcoholic  and  subsequent  acetous  fermentations  of  the  juice  of  ap- 


342  UNIVERSITY   OF   CALIFORNIA EXPERIMENT   STATION. 

pies,  is  hevo-rotatory,  and  contains  not  less  than  four  (4)  grams  of 
acetic  acid,  not  less  than  one  and  six  tenths  (1.6)  grams  of  apple  solids, 
of  which  not  more  than  fifty  (50)  per  cent  are  reducing  sugars,  and 
not  less  than  twenty-five  hundredths  (0.25)  grams  of  apple  ash  in  one 
hundred  (100)  cubic  centimeters,  (20°C.)  ;  and  the  water-soluble  ash 
from  one  hundred  (100)  cubic  centimeters  (20°C.)  of  the  vinegar  con- 
tains not  less  than  ten  (10)  milligrams  of  phosphoric  acid  (P205)  and 
requires  not  less  than  thirty  (30)  cubic  centimeters  of  decinormal  acid 
to  neutralize  its  alkalinity. 

2.  Wine  vinegar,  grape  vinegar,  is  the  product  made  by  the  alcoholic 
and  subsequent  acetous  fermentations  of  the  juice  of  grapes  and  con- 
tains, in  one  hundred  (100)  cubic  centimeters  (20°C),  not  less  than 
four  (4)  grams  of  acetic  acid,  not  less  than  one  (1.0)  gram  of  grape 
solids,  and  not  less  than  thirteen  hundredths  (0.13)  gram  of  grape 
ash. 

3.  Malt  vinegar  is  the  product  made  by  the  alcoholic  and  subsequent 
acetous  fermentations,  without  distillation,  of  an  infusion  of  barley 
malt  or  cereals  whose  starch  has  been  converted  by  malt,  is  dextro- 
rotatory, and  contains,  in  one  hundred  (100)  cubic  centimeters  (20°C.) 
not  less  than  four  (4)  grams  of  acetic  acid,  not  less  than  two  (2)  grams 
of  solids,  and  not  less  than  two  tenths  (0.2)  gram  of  ash;  and  the 
water-soluble  ash  from  one  hundred  (100)  cubic  centimeters  (20°C.)  of 
the  vinegar  contains  not  less  than  nine  (9)  milligrams  of  phosphoric 
acid  (P205)  and  requires  not  less  than  four  (4)  cubic  centimeters  of 
decinormal  acid  to  neutralize  its  alkalinity. 

4.  Sugar  vinegar  is  the  product  made  by  the  alcoholic  and  subse- 
quent acetous  fermentations  of  solutions  of  sugar,  sirup,  molasses,  or 
refiners'  sirup,  and  contains,  in  one  hundred  (100)  cubic  centimeters 
(20°C.)  not  less  than  four  (4)  grams  of  acetic  acid. 

5.  Glucose  vinegar  is  the  product  made  by  the  alcoholic  and  subse- 
quent acetous  fermentations  of  solutions  of  starch  sugar  or  glucose,  is 
dextro-rotatory,  and  contains,  in  one  hundred  (100)  cubic  centimeters 
(20°C),  not  less  than  four  (4)  grams  of  acetic  acid. 

6.  Spirit  vinegar,  distilled  vinegar,  grain  vinegar,  is  the  product  made 
by  the  acetous  fermentation  of  dilute  distilled  alcohol,  and  contains, 
in  one  hundred  (100)  cubic  centimeters  (20°C.)  not  less  than  four  (4) 
grams  of  acetic  acid. 

According  to  these  standards  the  word  "vinegar,"  without  qualifica- 
tion can  be  applied  only  to  the  product  made  from  apples  or  cider. 
This  is  not  in  accord  with  the  most  extended  usage  nor  with  the  funda- 
mental meaning  of  the  word.  The  word  "vinegar"  is  derived  from 
the  French  "vinaigre"  which  means  literally  "sour  wine,"  as  shown 
by  its  derivation  from  the  two  Latin  words  vinum=wme  and  acer= 
sour. 


Bulletin  227]  GRAPE  VINEGAR.  343 

If  the  word  vinegar,  unqualified,  be  used  at  all  as  a  legal  term,  it 
should  apply  only  to  the  product  of  grapes  and  wine.  This  is  justi- 
fied by  the  facts  that  historically  the  first  vinegar  was  wine  vinegar 
and  that  wine  vinegar  is  still  considered  by  most  competent  authorities 
as  the  best  vinegar.  The  error  in  the  United  States  Standards  is  due 
to  the  fact  that,  in  the  Eastern  States,  most  of  the  best  vinegar  is  made 
from  apples.  It  is  possible  that  good  cider  vinegar  is  better  than  that 
made  from  Labrusca  varieties  of  grapes  such  as  are  grown  in  the  East. 
It  is,  however,  inferior  in  flavor  and  strength  to  vinegar  made  from 
Vinifera  grapes  such  as  are  grown  on  the  Pacific  coast  and  in  the 
principal  grape  growing  regions  of  Europe  and  Asia. 

III.     CLASSES    OF    VINEGAR    AND    RAW    MATERIALS. 

The  various  kinds  of  vinegar  are  usually  classed  in  accordance  with 
the  raw  materials  from  which  they  are  derived. 

The  best  vinegars  are  those  which  are  made  from  grapes  and  apples. 
They  contain  besides  acetic  acid  to  which  they  owe  their  "sourness," 
certain  agreeable  flavors  and  aromas  derived  either  directly  from  the 
fruit  or  produced  from  substances  contained  in  the  fruit  by  the  alcoholic 
and  acetic  fermentations. 

Excellent  vinegars  are  also  made  from  malt  and  from  honey.  These 
are  wholesome  and  pleasing  but  of  less  character  or  quality  than  those 
made  from  wine  or  cider.  All  these  vinegars  are  suitable  for  domestic 
or  table  use. 

Vinegars  made  from  sugar,  molasses  or  glucose  are  inferior,  lacking 
in  flavor  or  quality  and  unsatisfactory  for  table  use. 

Spirit  vinegar,  made  from  distilled  alcohol,  is  little  more  than  dilute 
acetic  acid  and  lacks  the  aromas  and  flavors  which  are  characteristic 
of  good  table  vinegar.  It  can  be  produced  very  easily  and  cheaply  and 
where  pure  food  laws  are  not  enforced  it  is  used  to  counterfeit  better 
vinegar  by  adding  various  coloring  and  flavoring  matters.  It  seems 
doubtful  whether  this  product  should  be  entitled  to  the  appellation 
of  vinegar  at  all. 

IV.     WINE   VINEGAR. 

Wine  vinegar  has  a  specific  gravity  of  1.014  to  1.022  and  contains 
generally  from  6  per  cent  to  10  per  cent  of  acetic  acid  and  from  1.7 
per  cent  to  2.4  per  cent  of  extract.  It  contains  also  organic  acids  de- 
rived directly  from  the  grape,  of  which  the  principal  is  tartaric  in  the 
form  of  bitartrate  of  potash.  By  the  presence  of  bitartrate,  wine 
vinegar  is  distinguished  from  all  others.  The  acidity  due  to  these 
organic  acids  averages  about  .5  per  cent.  In  the  best  vinegar,  from 
1  per  cent  to  1\  per  cent  of  alcohol  remains  unconverted  into  acetic 
acid.      The  alcohol  is  necessary  to  prevent  loss  of  acetic  acid  during 


344  UNIVERSITY   OF   CALIFORNIA EXPERIMENT   STATION. 

the  making  and  to  increase  the  quality  in  aging  by  the  production  of 
acetic  ether  and  other  aromatic  compounds. 

Wine  vinegar,  in  common  with  all  others,  must  contain  at  least  4 
per  cent  of  acetic  acid  to  conform  with  the  legal  standard.  Most  wine 
vinegar  contains  more  than  this  amount — 6  per  cent  to  10  per  cent — 
and  is  stronger  than  either  cider  or  malt  vinegar.  The  strength  of 
commercial  vinegars  is  expressed  in  "grains"  or  numbers  which  in- 
dicate the  number  of  grains  of  sodium  bicarbonate  neutralized  by  one 
fluid  ounce  wine  measure.  The  percentage  of  acetic  acid,  that  is,  the 
number  of  grams  of  absolute  acid  in  100  cubic  centimeters  of  vinegar, 
is  obtained  by  multiplying  the  "grains,"  or  "number,"  by  0.1565. 
Table  VI  on  page  350  shows  the  percentage  represented  by  the  numbers 
most  commonly  used. 

A  30  grain  vinegar  has  4.7  per  cent  of  acidity  and  therefore  would 
satisfy  the  legal  requirements.  Unless  vinegars  are  bottled  and  pas- 
teurized, however  they  lose  strength  with  time.  Under  ordinary  con- 
ditions of  keeping  in  a  partially  filled  cask,  one  per  cent  of  acid  may 
be  lost  in  a  few  months.  Dealers,  therefore,  have  adopted  a  standard 
of  40  grains  as  the  minimum  for  commercial  vinegars.  In  determin- 
ing the  strength  of  a  wine  vinegar  3  grains  or  .5  per  cent  must  be 
deducted  from  the  observed  reading  on  account  of  the  fixed  organic 
acids. 

Vinegar  is  made  from  both  white  and  red  wine.  White  wine  vinegar 
is  generally  preferred.  Red  wine  vinegar  is  perhaps  equally  good  but 
is  usually  not  salable  until  it  has  been  decolorized,  and  the  process  of 
decolorizing  diminishes  its  flavor  and  aroma. 

V.     ALCOHOLIC    FERMENTATION. 

Vinegar  can  be  made  either  from  grapes  or  wine.  In  either  case 
the  acetifying  process  is  the  same.  If  grapes  are  used,  they  must  be 
first  made  into  good  wine.  The  methods  of  wine-making  described  in 
Bulletin  213  may  be  used  with  one  important  exception.  Sulfurous 
acid  should  not  be  used,  as  it  interferes  very  materially  with  the  trans- 
formation of  the  wine  into  vinegar.  This  makes  it  necessary,  especially 
in  warm  regions,  to  take  special  precautions  to  avoid  hot  fermentation 
and  the  "sticking"  of  the  fermenting  must.  This  is  accomplished  by 
using  small  fermenting  vats,  by  thorough  aeration  and  by  diluting  the 
must  to  20°  B.  when  necessary.  By  these  means  it  is  easy  to  obtain 
a  complete  transformation  of  the  sugar  into  alcohol  in  five  or  six  days, 
and  to  avoid  the  injurious  action  of  the  anaerobic  bacteria  which  pro- 
duce undesirable  flavors  in  the  wine  and  consequently  in  the  vinegar. 

On  the  other  hand,  the  great  care  used  in  wine-making  to  avoid  the 
action  of  aerobic  bacteria  is  not  necessary  if  the  wine  is  to  be  turned 
into  vinegar.     These  aerobic  bacteria  are  in  fact  the  cause  of  the  sub- 


Bulletin  227] 


GRAPE  VINEGAR. 


345 


sequent  fermentation  which  changes  the  alcohol  of  the  wine  into  the 
acetic  acid  of  the  vinegar. 

The  manufacture  of  vinegar  from  grapes,  therefore,  has  two  distinct 
stages.  First,  the  alcoholic  fermentation  by  which  the  sugar  is  changed 
into  alcohol  and  carbonic  acid  gas.  The  cause  of  this  fermentation  is 
yeast.  Second,  the  acetic  fermentation  by  which  the  alcohol  is  changed 
into  acetic  acid.     The  cause  of  this  fermentation  is  vinegar  bacteria. 

These  two  fermentations  cannot  take  place  together  and  care  should 
be  used  to  prevent  the  beginning  of  the  acetic  fermentation  before  the 
alcoholic  fermentation  is  finished.  While  the  yeast  is  working  vigor- 
ously, it  absorbs  the  oxygen  dissolved  in  the  must  and  replaces  it  with 
carbonic  acid  gas.  This  prevents  the  growth  of  vinegar  bacteria  which 
are  active  only  in  the  presence  of  abundant  free  oxygen.  If  anything 
stops  the  work  of  the  yeast  before  all  the  sugar  is  transformed,  acetic 
bacteria  may  develop  and  produce  acetic  acid.  Acetic  acid  in  quan- 
tities approaching  .5  per  cent  interferes  with  the  work  of  the  yeast  and 
at  1  per  cent  stops  it  entirely.  These  facts  are  shown  by  the  following 
experiments. 

*Table  I. 

Influence  of  acetic  acid  on  yeast  fermentations. 


Volatile  acid. 

Sugar. 

Nature   of   experiment. 

Added. 

At  end. 

In  must. 

At  end. 

Grape  must  16.1%  sugar  and  .5%  fixed  acid..^ 

Added  various  amounts  acetic  acid 

Inoculated  with  vigorous  pure  yeast 

Temperature  25°  C.    Duration  of  experiment 
26  days . 

a 
b 
c 

d 
e 

.10 
.25 

.40 

.50 
1.00 

.07 
.26 
.38 

.51 
1.01 

16.1 
16.1 
16.1 

16.1 
16.1 

.26 
.27 
.26 

6.00 
16.00 

J 

*  Most  of  the  experiment  work  of  this  bulletin  was  done  by  Mr.  W.  Cruess. 


This  shows  that  under  the  conditions  of  the  experiment  1  per  cent 
of  acetic  acid  completely  prevented  all  alcoholic  fermentation  and  that 
.5  per  cent  prevented  its  completion.  Smaller  amounts  had  no  effect. 
This  indicates  that  the  small  amounts  of  acetic  acid  which  would  be 
introduced  into  the  must  by  the  use  of  vinegar-sour  barrels,  buckets 
or  hoses  would  not  prevent  complete  alcoholic  fermentation  if  all  other 
conditions  were  favorable.  The  care  used  in  wine-making  to  remove 
all  traces  of  vinegar  is  therefore  not  necessary  if  the  wine  is  to  be 
turned  into  vinegar.  It  shows,  on  the  other  hand,  that  the  mixing  of 
vinegar  and  must  would  prevent  the  transformation  of  the  sugar  in  the 
latter. 


346 


UNIVERSITY   OF   CALIFORNIA EXPERIMENT   STATION. 


Table  II. 

Influence  of  the  presence  of  vinegar  bacteria  on  yeast  fermentation. 

A.     Sterilized  Must  inoculated  with  Pure  Yeast. 


Temperature  of 
fermentation. 

Sugar 
in  must. 

Sugar  remaining  after  five  days. 

Yeast  No.  1. 

Yeast  No.  2. 

a. 

28°  C 

20%  B. 

.38% 

.50% 

B. 

Sterilized  Must  inoculated  with  Pure  Yeast  and  Vinegar  Bacteria. 

Under  the  conditions  of  the  experiment  the  yeast  fermentation  was 
just  as  complete  in  the  presence  of  the  bacteria  as  in  their  absence. 
Compare  (a)  and  (d) .  The  cause  of  this  was  that  the  conditions  were 
favorable  to  yeast  fermentation  and  that  the  latter  produced  conditions 
(absence  of  oxygen)  unfavorable  to  the  bacteria  which  therefore  did 
not  develop.  In  practice,  therefore,  if  care  is  taken  to  keep  conditions 
favorable  to  the  yeast  during  the  alcoholic  fermentation  the  presence 
of  vinegar  bacteria  is  not  harmful. 

On  the  other  hand,  if  conditions  unfavorable  to  the  yeast  are  allowed 
to  exist,  the  bacteria  may  increase  and  produce  sufficient  acetic  acid  to 
stop  alcoholic  fermentation  before  the  sugar  is  all  transformed.  This 
is  shown  by  Experiment  III. 

Table  III. 

Influence  of  the  presence  of  vinegar  bacteria  and  acid  on  yeast  fermentation. 


Volatile  acid. 

Sugar. 

Nature   of    experiment. 

Added. 

At  end. 

In  must. 

At  end. 

Grape  must  16,1%  sugar  and  .5%  fixed  acid..' 

Added  various  amounts  acetic  acid 

Inoculated    with    yeast    and    vinegar    bac- 
teria    _  _           _    _    _                     ___ 

a 
b 

c 

(I 

.10 

.25 
.40 
.50 

.23 
.49 

2.20 

2.01 

16.1 
16.1 

16.1 

16.1 

.28-) 
.26 

5.30 

Temperature  24°  C.    Duration  of  experiment 
26  days 

7.50 

This  shows  that  while  .4  per  cent  of  acetic  acid  alone  was  not  enough 
to  prevent  a  complete  alcoholic  fermentation  (see  Exp.  Ic)  it  had  suffi- 
cient unfavorable  influence  on  the  yeast  to  allow  bacteria  when  present 
to  grow  and  produce  more  acetic  acid  and  thus  prevent  the  transforma- 
tion of  all  the  sugar.     This  shows  that  in  practice,  where  vinegar  bac- 


Bulletin  227] 


GRAPE  VINEGAR, 


347 


teria  are  always  present,  it  is  not  safe  to  allow  the  must  to  be  con- 
taminated with  even  .4  per  cent  of  acetic  acid  before  the  alcoholic 
fermentation  is  complete.  Reasonable  care,  therefore,  should  be  taken 
to  prevent  any  notable  quantities  of  acetic  acid  getting  into  the  must 
or  crushed  grapes  before  alcoholic  fermentation  is  complete. 

This  will  be  accomplished  if  all  mixing  of  unfermented  or  partially 
fermented  sweet  juice  with  vinegar  or  partially  acetified  wine  is  avoided. 
Vessels  and  casks  that  have  been  used  for  the  acetic  fermentation  or 
for  holding  vinegar  can  be  used  for  the  alcoholic  fermentation  provid- 
ing they  are  well  rinsed  with  water  before  use. 

Under  favorable  conditions,  vinegar  bacteria  will  attack  sugar  and 
produce  acetic  acid  directly.  Under  the  conditions  of  vinegar  mak- 
ing, however,  this  action  is  very  slow  and  any  sugar  left  in  the  wine 
after  the  start  of  acetification  may  be  considered  as  lost.  This  is  shown 
by  the  experiments  summarized  in  the  following  table. 

Table  IV. 
Influence  of  vinegar  bacteria  on  the  sugar  in  wine. 


Sample. 

Wine. 

At  3  weeks. 

At  10  weeks. 

Culture. 

Alcohol. 

Sugar. 

Volatile 

acid. 

Sugar. 

Volatile 
Acid. 

Sugar. 

Volatile 
Acid. 

No.  78 J 

r 

No.  76 j 

A. 
B. 
C. 

A. 
B. 
C. 

9.52 
7.93 
7.32 

9.50 
7.93 
7.32 

4.10 

6.80 
4.75 

4.10 
6.80 
4.75 

.06 
.05 
.05 

.06 
.05 
.05 

410 
6.60 
4.54 

4.12 
6.66 
4.60 

.08 

.48 

5.40 

.16 

.10 

2.80 

4.20 
6.59 
4.60 

4.26 
.10* 

4.40 

6.10 
5.90 
6.40 

.19 

.20 

6.20 

*  Disappearance  of  sugar  due  to  yeast  contamination. 

Culture  No.  78  was  isolated  from  wine  vinegar  and  Culture  No.  76 
from  cider  vinegar.  In  ten  weeks  neither  of  them  had  had  any  appre- 
ciable action  on  the  sugar.  The  cider  vinegar  bacteria,  moreover,  had 
been  unable  to  attack  the  alcohol  in  the  stronger  wines. 

Further  details  of  the  methods  of  alcoholic  fermentation  may  be 
obtained  from  Bulletin  213. 


VI.     ACETIC     FERMENTATION. 

If  wine  containing  less  than  14  per  cent  of  alcohol  is  exposed  freely 
to  the  air  it  soon  becomes  covered  with  a  film,  the  alcohol  disappears, 
is  replaced  by  acetic  acid,  and  the  liquid  is  converted  into  vinegar. 

This  film,  the  Mycoderma  aceti  of  Pasteur,  consists  of  bacteria  coher- 
ing by  means  of  a  glutinous  sheath  surrounding  each  cell.  If  the  film 
is  undisturbed,  the  liquid  remains  clear  until  converted  into  vinegar. 


348 


UNIVERSITY   OF   CALIFORNIA EXPERIMENT   STATION. 


If  disturbed,  portions  may  sink,  new  films  form  and  finally,  a  large 
gelatinous  mass,  the  ' '  mother  of  vinegar, ' '  may  form  in  the  liquid. 

Sometimes,  especially  in  liquids  containing  sugar  and  more  than 
14  per  cent  of  alcohol,  such  as  sweet  wines,  the  film  formed  consists, 
not  of  bacteria,  but  of  a  yeast-like  fungus  known  as  "Mycoderma  vini," 
or  * '  wine-flowers. ' '  This  organism  is  totally  different  from  the  vinegar 
germ  and  is  harmful,  destroying  the  alcohol  but  not  producing  vinegar. 

Films  due  to  wine  flowers  are  thicker  and  whiter  than  those  due  to 
vinegar  bacteria,  and  are  easily  recognized  by  the  experienced  eye  and 
with  certainty  by  the  use  of  a  microscope. 


Fig.   1. — 1.  Yeast.     2.  Wine  Flowers.      3.  Vinegar  Bacteria. 

Wines,  which  have  been  sterilized,  often  remain  without  acetifying 
for  a  considerable  time.  Those  containing  traces  of  sulfurous  acid 
acetify  slowly  and  with  difficulty.  Ordinarily,  at  warm  temperatures, 
other  exposed  wines  develop  a  bacterial  film  very  rapidly  owing  to  the 
presence  of  acetic  bacteria  in  almost  all  wines.  There  are  several  or 
many  species  of  vinegar  bacteria,  but  those  which  occur  usually  in 
wine,  and  to  which  the  spontaneous  acetifying  of  wine  is  due,  resemble 
each  other  very  closely  in  their  conditions  of  growth,  and  no  differences 
have  been  noted  in  the  quality  of  vinegar  which  they  produce. 

All  species  are  strongly  aerobic,  that  is,  they  grow  rapidly  only  when 
freely  supplied  with  air  or  oxygen.  They  grow  best  at  a  temperature 
of  about  90°  F.  to  93°  F.  Some  of  them  will  grow  near  40°  F.  but  at 
low  temperatures  their  growth  is  very  slow.  Above  93°  F.  their  activ- 
ity diminishes  and  at  107°  or  108°  all  action  ceases. 

Their  principal  action  on  the  wine  is  the  formation  of  acetic  acid 
from  the  ordinary  or  ethyl  alcohol.  They  also  attack  other  alcohols  and 
even  sugars  with  the  production  of  various  acids.  These  reactions 
however,  are  less  rapid  and  of  little  bearing  on  practice  except  in  so 
far  as  they  may  account  in  part  for  the  superior  aroma  and  quality 
of  vinegars  made  by  the  slow  process. 

The  presence  of  too  much  alcohol  prevents  the  growth  of  vinegar 
bacteria,  the  limit  being  about  14  per  cent  by  volume  under  manufac- 
turing conditions.     At  14  per  cent  and  above,  the  film  forms  with  dif- 


Bulletin  227]  GRAPE  VINEGAR.  349 

ficulty  and  the  oxidation  of  the  alcohol  is  incomplete,  aldehyde  and 
undesirable  products  being  formed.  Acetic  acid  in  amounts  above  10 
per  cent  or  12  per  cent  is  moreover  antiseptic  to  the  bacteria  and  pre- 
vents their  growth.  Below  14  per  cent  of  alcohol,  the  bacteria  develop 
readily  and  produce  in  suitable  solutions,  besides  acetic  acid,  agreeable 
ethers  which  are  more  abundant  when  the  oxidation  is  slow.  When 
the  alcohol  falls  below  1  per  cent  or  2  per  cent  the  bacteria  attack 
these  ethers  and  finally  the  acetic  acid  itself  which  is  completely  oxi- 
dized to  carbonic  acid  and  water. 

The  addition  of  a  new  supply  of  wine  containing  alcohol,  however, 
immediately  arrests  this  action.  In  practice,  the  acetification  should 
be  stopped  as  soon  as  the  alcohol  has  fallen  to  one  or  two  per  cent, 
otherwise  there  is  a  loss  of  flavor  and  of  acetic  acid  which  may  continue 
until  the  vinegar  is  completely  destroyed. 

VII.     YIELD   OF   VINEGAR. 

In  changing  grapes  into  vinegar  there  is  a  certain  amount  of  loss 
at  every  stage  of  the  process.  Some  of  this  loss  is  unavoidable  but 
some  can  be  saved  by  careful  work.  There  is,  therefore,  a  theoretical 
maximum  yield  based  on  the  composition  of  the  grapes  which  can 
never  be  quite  reached.  There  is  also  a  maximum  practical  yield 
which  the  manufacturer  should  attempt  to  reach.  The  maximum 
theoretical  and  practical  yields  will  differ  for  different  grapes  owing 
to  differences  in  the  amounts  of  stems,  seeds  and  skins,  and  also  owing 
to  variations  in  the  percentage  of  fermentable  sugars.  The  follow- 
ing table  gives  an  approximation  of  the  average  for  grapes  grown  in 
California  showing  20°  Balling: 

Table  V. 

Yield  of  2,000  pounds  of  grapes  of  20    Bal. 

A.     Yield,  of  Must  from  2000  pounds   of   Grapes. 

Theoretical  average  yield  of  stems,  seeds  and  stems 200  pounds 

Theoretical  average  yield  of  pulp  (or  must) 200  gallons 

Maximum  yield  of  must  in  practice 140  to  160  gallons 

Average  maximum  yield  of  must 150  gallons 

B.     Yield  of  Wine  from  150  gals,  of  Must  at  20°  Bal. 
Maximum  yield  of  alcohol,  in  practice,  47%  of  sugar,  =  8.78.  by  weight  =  11%  by 

volume. 
Maximum  yield  of  wine,  =  143  gallons,  at  8.78%  by  weight. 

C.     Yield  of  Vinegar  from  U/3  gals,  of  Wine  of  8.78%  Alcohol. 
Theoretical  yield  of  acetic  acid,  =  11.4%. 
Maximum  yield  in  practice,  85%  =9.8%. 
Maximum  yield  of  vinegar,  135  gals,  of  9.8%  =  63  grains. 

One  ton  of  grapes  of  20°  B.  should  then  on  the  average  yield  135 
gallons  of  vinegar  of  9.8-  per  cent  acetic  acid.  It  may  be  greater  or 
less  than  this  according  as  the  grapes  contain  more  or  less  sugar.  This 
yield  may  be  diminished  by  imperfect  crushing  and  pressing  of  the 
grapes  whereby  more  must  is  left  in  the  pomace.  Alcohol  may  be 
lost  by  imperfect  or  improper  fermentation,  in  which  case  the  vinegar 


350 


UNIVERSITY  OF   CALIFORNIA EXPERIMENT   STATION. 


will  be  weaker.  The  greatest  difference  between  the  theoretical  and 
the  actual  yield  is  in  the  change  from  wine  into  vinegar.  This  is  be- 
cause one  or  two  per  cent  of  alcohol  remains  unconverted  in  the  vine- 
gar, and  because  during  the  process  there  is  a  considerable  loss  of 
alcohol  and  acetic  acid  by  evaporation,  and  by  reactions  within  the 
liquid  which  produce  other  substances  at  the  expense  of  the  alcohol 
and  acetic  acid.  If  the  temperature  during  acetiflcation  is  too  high, 
or  if  the  acetic  bacteria  are  allowed  to  act  too  long,  this  loss  may  be 
much  increased. 

By  allowing  the  crushed  grapes  to  ferment  on  the  skins  before 
pressing,  a  somewhat  larger  volume  of  wine  and  therefore  of  vinegar 
may  be  obtained.  This  may  amount  to  150  or  160  gallons  of  vinegar 
from  a  ton  of  grapes.  The  vinegar,  however,  will  be  darker  colored 
and,  in  the  case  of  red  grapes,  red.  This  color  can  be  removed,  but 
the  decoloration  is  difficult  and  involves  some  loss  of  quality. 

Fermentation  for  twenty-four  hours  on  the  skins  will  much  facili- 
tate the  extraction  of  the  juice  without,  except  in  the  case  of  grapes 
very  rich  in  coloring  matter,  reddening  the  juice  very  much. 


Table  VI. 
Strength  of  vinegar  from  musts  of  various  degrees  Balling. 


Wine    (alcohol). 

Vinegar    (acetic  acid). 

Must  (sugar). 
Balling  degrees. 

By  volume, 
per  cent. 

By  weight, 
per  cent. 

By  weight, 
per  cent. 

Grains. 

15.0 
15.5 
16.0 
16.5 
17.0 
17.5 
18.0 
18.5 
19.0 
19.5 
20.0 
20.5 
21.0 
21.5 
22.0 
22.5 
23.0 

7.55 

7.87 

8.22 

8.60 

8.88 

9.20 

9.56 

9.90 

10.28 

10.60 

10.99 

11.34 

11.69 

12.00 

12.39 

12.75 

13.10 

6.06 
6.32 
6.60 
6.91 
7.14 
7.39 
7.69 
7.96 
8.27 
8.53 
8.85 
9.14 
9.42 
9.66 
9.99 
10.28 
10.57 

6.7 

7.0 

7.3 

7.7 

7.9 

8.2 

8.5 

8.8 

9.2 

9.5 

9.8  -, 
10.1 
10.5 
10.7 
11.1 
11.4 
11.7 

43 
45 
47 
49 
51 
53 
55 
57 
59 
61 
63 
65 
67 
69 
71 
73 
75 

VIII.     PROCESSES  OF  MANUFACTURE. 

There  are  many  processes  by  which  an  alcoholic  liquid  may  be  changed 
into  vinegar  but  they  all  consist  essentially  in  exposing  the  liquid  to 
the  action  of  vinegar  bacteria  in  the  presence  of  an  abundant  supply 
of  air  at  a  suitable  temperature.  Some  of  them  are  based  on  the  old 
Orleans  or  slow  process,  others  on  the  German  or  rapid  process,  and  the 
remainder  are  attempts  to  combine  the  good  qualities  of  both. 


Bulletin  227] 


GRAPE  VINEGAR. 


351 


The  slower  processes  give  the  best  and  most  highly  flavored  vinegars 
and  are  alone  to  be  recommended  for  the  manufacture  of  wine  vinegar 
of  fine  quality. 

Whatever  the  process  adopted,  the  wine  should  be  clear  and  dry, 
that  is,  should  contain  no  sediment  nor  unfermented  sugar.  Young 
wine  should  be  kept  and  racked  off  until  it  has  deposited  all  yeast  and 
gross  lees.  Then,  if  necessary,  it  should  be  filtered  and  diluted  with 
pure  water  to  about  10  or  12  per  cent  of  alcohol. 

a.  Domestic  process.  For  home  use  or  for  manufacture  on  a  small 
scale,  the  vinegar  is  most  conveniently  made  in  ordinary  wooden  casks. 
These  casks  may  be  of  any  convenient  size  from  10  to  50  gallons  or 
even  larger.  Fifty  gallon  barrels  are  perhaps  the  best.  These  barrels 
should  be  furnished  with  some  form  of  funnel  for  putting  in  the  wine 
without  disturbing  the  bacterial  film  and  with  a  spigot  for  drawing 
off  the  vinegar.  A  hole  for  ventilation  should  be  bored  in  each  head, 
one  just  above  the  middle  and  the  other  near  the  top.  These  holes 
should  be  covered  with  varnished  metal  netting  to  prevent  the  entrance 
of  vinegar  flies.     Fig.  2  shows  a  convenient  arrangement. 


Vf 


Fig.   2. — Cask  for  Vinegar  Fermentation. 

The  wine  is  poured  into  the  barrel  through  the  funnel  (F)  which 
is  furnished  with  a  long  glass  tube  (G)  which  extends  nearly  to  the 
bottom  of  the  cask.  The  barrel  is  filled  only  to  the  line  (L),  about 
the  middle,  in  order  to  give  as  large  a  surface  for  the  bacterial  film  to 
cover  as  possible.  The  bacteria  are  supplied  with  the  necessary  oxygen 
by  a  current  of  air  which  entering  at  A  passes  over  the  surface  of  the 
liquid  and  escapes  at  B.  The  tube  S  serves  for  drawing  off  the  fin- 
ished vinegar  and  as  an  indicator  of  level.  It  may  be  replaced  by  a 
wooden  spigot. 


352  UNIVERSITY  OF   CALIFORNIA EXPERIMENT  STATION. 

In  starting  the  process,  about  10  per  cent  of  good  vinegar  is  first 
placed  in  the  cask  (2  to  3  gallons  for  a  fifty  gallon  barrel).  The  clear 
wine  is  then  poured  in  until  the  surface  of  the  liquid  is  nearly  level 
with  the  air  hole  in  the  head.  The  wine  is  best  added  in  fractional 
parts  of  one  fourth  to  one  third  of  the  total  amount,  at  intervals  of 
one  week.  The  use  of  the  vinegar  is  to  render  the  liquid  strongly  acid 
and  thus  prevent  the  growth  of  injurious  bacteria  and  other  organisms. 
If  young  and  unpasteurized,  it  also  supplies  an  abundant  inoculation 
of  vinegar  bacteria. 

The  cask  should  be  placed  on  a  solid  stand  and  firmly  fixed.  Any 
movement  of  the  cask  is  apt  to  disturb  the  surface  film  and  interfere 
with  the  proper  work  of  the  bacteria.  Bacteria  which  sink  to  the 
bottom  do  not  produce  acetic  acid  and,  if  plentiful,  may  seriously 
depreciate  the  quality  of  the  vinegar. 

The  higher  the  temperature  of  the  liquid,  under  93°  F.,  the  more 
rapid  the  process  of  acetification.  The  vinegar  room,  therefore,  should 
be  kept  near  70°  F.  if  practicable.  Lower  temperatures  retard  the 
process  unduly  and  much  higher  depreciate  the  quality.  It  is  advis- 
able to  warm  the  wine  to  85°  F.  or  90°  F.  before  putting  it  in  the  casks. 

At  the  end  of  one,  two  or  three  months,  according  to  the  temperature, 
the  degree  of  aeration  and  the  strength  of  alcohol,  the  vinegar  fer- 
mentation should  be  finished.  If  the  wine  is  very  high  in  alcohol  and 
the  average  temperature  of  the  room  below  60°  F.  the  time  may  be 
much  prolonged.  In  an  ordinary  barrel  without  the  extra  air  holes 
in  the  ends  it  may  require  a  year  or  longer  to  completely  transform 
the  wine  into  vinegar. 

As  soon  as  the  acetic  fermentation  is  complete,  that  is,  when  all  the 
alcohol  has  been  changed  into  acetic  acid  except  about  1  per  cent  or 
2  per  cent  the  vinegar  should  be  removed  from  the  barrel. 

This  is  done  by  drawing  off  through  the  spigot.  About  one  tenth  of 
the  vinegar  should  be  left  in  the  barrel,  which  should  be  disturbed 
as  little  as  possible  in  order  not  to  destroy  the  bacterial  surface  film. 
A  new  supply  of  wine  is  then  introduced  by  means  of  the  funnel  and 
glass  tube.  This  wine  should  be  introduced  carefully,  in  order  to, 
disturb  the  sediment  and  bacterial  film  as  little  as  possible.  As  soon 
as  this  new  supply  is  acetified  it  should  be  removed  and  the  process 
repeated  until  the  accumulation  of  sediment  makes  it  necessary  to 
clean  the  barrel. 

b.  Industrial  methods.  The  method  just  described  is  essentially  the 
old  Orleans  method  which  is  still  used  to  produce  fine  vinegars  on  a 
large  scale.  It  has,  however,  many  defects  for  manufacturing  on  an 
industrial  scale.  It  is  slow  and  laborious,  and  there  is  a  considerable 
loss  of  material  by  evaporation  and  by  the  formation  of  large  masses 


Bulletin  227]  GRAPE  VINEGAR.  353 

of  gelatinous  "mother  of  vinegar,"  which  depreciates  the  quality  and 
necessitates  expensive  cleanings  of  the  casks. 

Various  methods,  based  on  the  researches  of  Pasteur,  have  been 
devised  to  overcome  the  defects  of  the  old  method  while  retaining  its 
advantages.  That  of  Claudon  is  one  of  the  best  and  will  serve  to 
exemplify  all.  The  vinegar  vat  shown  in  Fig.  3  illustrates  the  prin- 
ciple of  the  Claudon  apparatus. 

It  consists  essentially  of  a  wide,  shallow,  covered,  rectangular  vat, 
furnished  with  numerous  openings  near  the  top  {a)  by  which  the  en- 
trance of  air  can  be  facilitated  and  regulated.  This  vat  is  filled  to  near 
the  bottom  of  the  air  vents  with  a  mixture  of  four  parts  of  good  new 
vinegar  and  six  parts  of  wine  which  has  been  pasteurized  at  140°  F., 
and,  when  necessary,  filtered.  On  top  of  this  liquid  is  floated  a  light 
wooden  grating  (/)  which  helps  to  support  the  bacterial  film  and  pre- 
vents its  breaking  and  submerging  during  the  various  operations. 
When  filled,  the  process  is  started  by  placing  a  small  quantity  of  a 


Fig.  3. — Sketch  illustrating  the  principles  of  the  Pasteur  method. 

good  bacterial  film  on  top  of  the  liquid  which  soon  becomes  completely 
covered,  when  the  proper  conditions  of  temperature  and  aeration  are 
maintained. 

Each  acetifying  vat  is  connected  with  a  small  measuring  vat  (B) 
from  which  the  proper  amount  of  liquid  is  taken  every  day  after  a 
corresponding  amount  of  vinegar  has  been  removed.  These  two  vats 
constitute  a  unit,  several  of  which,  usually  six,  are  united  in  a  battery. 
A  factory  includes  several  of  these  batteries. 

The  batteries  are  fed  from  a  large  vat  or  reservoir,  where  the  mix- 
ture of  wine  and  vinegar  is  prepared  and  stored.  The  vinegar  drawn 
from  the  batteries  runs  directly  to  filters,  from  there  to  a  pasteurizer, 
and  thence  to  the  storage  casks.  The  output  of  these  batteries  is  from 
two  to  five  times  as  great  per  square  yard  of  acetifying  surface  as 
that  of  the  old  methods ;  the  cost  of  operation  is  considerably  less,  the 
loss  by  evaporation  much  reduced,  and  the  quality  equal  and  much 
more  under  the  control  of  the  manufacturer. 


354 


UNIVERSITY   OP   CALIFORNIA EXPERIMENT   STATION. 


c.  Rapid  or  German  process.  The  chief  advantage  of  the  Claudon 
and  similar  improved  methods  is  that  a  larger  surface  is  exposed  to 
the  action  of  the  bacterial  film  and  the  process  thus  hastened.  The 
Rapid  or  German  methods  extend  this  principle  further,  and  attempt 
to  give  the  greatest  surface  possible  for  the  action  of  the  bacterial  film. 


Fig.  4. — Vinegar  Generator. 

V.  Mass  of  beech  chips  over  which  the  wine  trickles  from  the  small  holes  in  the 
false  head  H  becoming  acetified  and  passing  through  holes  in  the  false  bottom  H. 
E.  Tilting  trough  for  the  intermittent  supply  of  wine.  a.  Course  of  air  ;  w.  course 
of  wine  ;   t.  thermometer. 

This  is  accomplished  by  what  is  known  as  a  Vinegar  Generator,  of 
which  there  are  many  forms.  A  common  form  of  generator  consists 
of  a  tall  cylindrical  or  slightly  conical  wooden  vat  provided  with  a 
perforated  false  head  a  few  inches  from  the  bottom,  and  another,  simi- 
lar in  structure,  at  the  same  distance  from  the  top.      The  space  be- 


Bulletin  227]  GRAPE  VINEGAR.  355 

tween  these  two  false  heads  is  filled  with  long  thin  chips  or  shavings 
of  beech  wood  which  have  been  thoroughly  extracted  first  with  water 
and  then  with  good  strong  vinegar. 

Instead  of  wood  shavings,  other  substances  such  as  corn  cobs  and 
grape  stems  have  been  used  successfully.  The  material  should  be  taste- 
less, finely  divided  and  sufficiently  resistant  not  to  pack  too  tightly 
during  the  process. 

In  operation,  the  liquid  to  be  acetified  is  distributed  over  the  top 
false  head  intermittently  in  small  amounts.  This  intermittent  supply 
is  accomplished  by  various  automatic  devices.  If  the  supply  is  con- 
tinuous, the  liquid. tends  to  run  in  streams  or  currents  in  certain  parts 
of  the  vat  and  much  of  the  acetifying  surface  is  lost;  if  too  rapid,  the 
bacterial  film  is  removed  from  the  upper  part  of  the  mass  of  beech 
chips  and  only  the  lower  part  is  effective. 

From  the  false  head,  the  liquid  passes  through  numerous  small  holes 
to  the  mass  of  beech  chips,  over  which  it  trickles  slowly  and  is  acetified 
by  means  of  the  bacterial  film  which  covers  them.  By  the  time  it 
reaches  the  lower  false  head,  the  alcohol  is  in  greater  or  less  amount 
converted  into  acetic  acid.  Usually,  the  liquid  must  pass  through 
from  two  to  five  times  or  through  an  equal  number  of  vats  before  it 
is  completely  changed  into  vinegar.  The  number  of  passages  depends 
on  the  temperature,  the  amount  of  alcohol  present,  the  height  of  the 
acetifying  column,  the  rapidity  of  the  flow,  and  on  the  perfection  of 
the  apparatus.  The  maximum  vinegar  strength  is  obtained  when  the 
alcohol  has  fallen  to  1  per  cent.  A  passage  through  the  generator  after 
this  will  decrease  the  strength  by  destroying  acetic  acid. 

Oxygen  is  supplied  by  the  air,  which,  entering  holes  in  the  vat  below 
the  lower  false  head,  passes  through  numerous  holes  in  the  latter, 
through  the  interstices  between  the  chips  and  out  through  short  tubes 
fixed  in  the  upper  false  head  and  holes  in  the  top.  The  passage  of  air 
is  insured  by  the  heating  of  the  interior  due  to  the  fermentation.  It 
can  be  regulated  by  the  number  and  diameter  of  the  air  holes. 

The  temperature,  which  should  be  close  to  85°  F.,  must  be  care- 
fully regulated.  If  the  temperature  rises  too  high,  the  loss  by  evap- 
oration will  be  much  increased,  if  too  low  the  acetification  will  be 
retarded.  Many  modifications  of  this  method  exist,  having  principally 
for  their  objects  the  more  complete  regulation  of  the  temperature  and 
air  supply,  the  recuperation  of  the  volatile  matters,  and  the  avoidance 
of  the  need  of  repassing  the  liquid  through  different  acetifying  columns. 


356  UNIVERSITY  OF   CALIFORNIA EXPERIMENT   STATION. 

IX.     AFTER-TREATMENT. 

a.  Clearing.  As  soon  as  the  acetic  fermentation  is  complete,  that  is, 
when  all  the  alcohol  but  1  per  cent  to  2  per  cent  has  been  converted 
into  acetic  acid,  all  bacterial  or  other  fermentative  action  should  be 
stopped.  The  vinegar,  as  it  comes  from  the  casks  or  other  acetifying 
vessels,  will  be  nearly  clear  if  it  has  been  made  from  clear  wine.  In 
this  case  it  may  be  used  immediately  without  further  treatment.  It 
does  not,  however,  attain  its  finest  qualities  until  it  has  been  aged.  In 
any  case,  if  not  quite  free  from  perceptible  cloudiness  it  should  be 
filtered.  Bag,  tissue,  or  pulp  niters  may  be  used,  providing  they  are 
so  constructed  that  the  vinegar  does  not  come  in  .contact  with  any 
metal  except  pure  tin  in  its  passage. 

b.  Decoloration.  Vinegar  will  be  generally  a  little  lighter  in  color 
than  the  wine  from  which  it  is  made.  If  this  is  red  wine,  however,  it 
will  still  be  too  dark  for  commercial  purposes.  Dark  and  red  vinegar 
may  be  decolorized  by  means  of  animal  charcoal.  This  charcoal  should 
be  pure  and  tasteless.  That  specially  prepared  for  the  decoloration 
of  pink  wines  is  the  best.  It  is  treated  with  acid,  thoroughly  washed 
with  water  and  kept  in  the  form  of  a  moist  paste.  It  varies  very  much 
in  its  decolorizing  power  and  a  preliminary  test  should  be  made  to 
determine  the  amount  to  use.  From  2  to  6  pounds  for  100  gallons 
will  usually  be  necessary  according  to  the  amount  of  color  to  be  de- 
stroyed and  the  decolorizing  power  of  the  sample.  The  charcoal  is 
thoroughly  stirred  up  in  the  vinegar  just  before  filtration.  As  char- 
coal diminishes  the  flavor  and  quality  to  some  extent,  it  is  better  to 
decolorize  the  wine  before  acetification  if  white  vinegar  is  required. 

The  color  may  be  too  light,  in  which  case,  it  may  be  brought  to  any 
required  depth  by  the  use  of  a  little  caramel  or  burnt  sugar. 

c.  Pasteurization.  Strong,  clear,  well  made  vinegar  may  be  stored 
in  casks  in  a  cool  place  until  ready  for  use.  Any  unfavorable  conditions 
of  temperature  or  handling  are,  however,  liable  to  depreciate  its  quality 
and  strength. 

This  depreciation  is  due  to  the  action  of  vinegar  bacteria  and  other 
organisms.  If  the  vinegar  is  to  be  aged,  therefore,  it  is  safer  and 
better  to  pasteurize  it  as  soon  as  acetification  and  clearing  are  complete. 
This  is  done  by  heating  momentarily  to  140°  F.  to  destroy  all  organisms 
in  the  liquid.  The  barrels  into  which  the  sterilized  vinegar  passes 
should  be  freshly  steamed  before  use.  Any  of  the  ordinary  forms  of 
pasteurizers  may  be  used,  providing  all  surfaces  with  which  the  vinegar 
comes  in  contact  consist  of  pure  tin  or  other  metal  attacked  with  diffi- 
culty by  acetic  acid.  The  vinegar  should  come  out  of  the  pasteurizer 
cool  and  the  receiving  barrel  should  be  completely  filled,  bunged  tight 
and  stored  in  a  cool  cellar. 


Bulletin  227]  GRAPE  VINEGAR.  357 

d.  Aging.  The  aging  of  vinegar  is  very  similar  in  its  purpose  and 
effects  to  the  aging  of  wine.  Stored  under  proper  conditions,  the 
quality  of  the  vinegar  improves  very  much  for  months,  acquiring  its 
maximum  quality  in  one  or  two  years.  It  is  only  by  aging  that  it 
acquires  the  special  aroma  which  distinguishes  good  wine  vinegar  from 
all  others. 

The  clear,  pasteurized  vinegar,  placed  in  sterilized,  tightly-bunged 
casks,  is  stored  immediately  in  a  cool  cellar  where  the  temperature  is 
fairly  uniform.  It  is  not  necessary  to  rack  it  or  draw  it  off  more  than 
once  in  six  months  as  good  vinegar  should  deposit  but  little  sediment. 
If  a  large  quantity  of  sediment  is  produced,  it  is  usually  a  sign  of 
unfavorable  bacterial  changes. 

e.  Fining,  Filtering  and  Bottling.  When  a  wine  vinegar  has  been 
brought  to  perfection  by  careful  manufacture  and  sufficient  aging,  it 
should  be  bottled.  Only  in  this  way  can  it  usually  be  sold  for  a  price 
commensurate  with  its  quality  and  capable  of  giving  a  profit  on  the  cost 
of  preparation. 

Before  bottling  it  must  be  perfectly  bright.  The  requisite  bright- 
ness may  be  obtained  by  filtration  or  fining.  Vinegar  is  somewhat  more 
difficult  to  fine  than  wine  and  the  best  results  are  obtained  by  the 
use  of  isinglass.  This  is  used  at  the  rate  of  from  one  half  to  three 
fourths  of  an  ounce  of  isinglass  to  10G  gallons  of  vinegar. 

The  isinglass  is  cut  into  small  pieces  and  soaked  for  twelve  to  twenty- 
four  hours  in  a  little  water  containing  acetic  or  tartaric  acid  equal  in 
weight  to  the  isinglass  used.  When  thoroughly  soft  it  is  then  rubbed 
several  times  through  a  fine  sieve,  gradually  adding  a  little  more  water 
until  a  perfectly  fluid  liquid  is  obtained.  This  fluid  is  then  well  mixed 
with  a  little  vinegar  and  thoroughly  stirred  into  the  cask.  With  some 
vinegars  it  is  necessary  to  add  a  little  tannin,  from  one  half  to 
one  seventh  the  amount  of  the  isinglass  used.  This  tannin  should  be 
added  at  least  twenty-four  hours  before  the  finings. 

When  the  finings  have  settled  and  the  vinegar  is  perfectly  bright 
it  is  ready  for  bottling.  The  bottles  after  filling  and  corking  should 
be  pasteurized  by  heating  in  a  water  bath  to  140°  F.  Vinegar  treated 
in  this  way  will  keep  for  years  without  deteriorating. 

x.     DISEASES. 

Vinegars  may  show  various  defects,  some  of  which  are  due  to  im- 
perfections of  the  raw  material  and  others  to  mistakes  or  accidents 
during  the  manufacture.      The  latter  are  known  as  diseases. 

a.  Secondary  fermentation.  The  only  fermentations  which  should 
take  place  in  vinegar  making  are  the  yeast  fermentation  by  which  the 
sugar  is  changed  into  alcohol  and  the  bacterial  fermentation  by  which 
the   alcohol  is  changed  into  acetic   acid.      Other  fermentations  may 


358  UNIVERSITY   OP   CALIFORNIA EXPERIMENT   STATION. 

occur,  however,  before,  during  or  after  these,  and  are  all  to  be  avoided 
as  harmful.  The  injurious  fermentations  of  grapes  and  wine  are  dis- 
cussed in  Bulletin  213. 

As  already  pointed  out  the  true,  useful  vinegar  bacteria  themselves, 
under  certain  circumstances,  produce  injurious  fermentations.  The 
bacteria  of  the  acetifying  film  gradually  sink  as  they  grow  old  or  are 
disturbed  by  shaking.  They  accumulate  at  the  bottom  of  the  liquid 
and  form  a  gelatinous  mass  or  zooglea.  In  this  mass,  which  is  called 
"mother  of  vinegar,"  the  action  of  the  bacteria  is  very  different  from 
that  of  the  surface  film.  They  are  deprived  of  oxygen  and  can  not 
therefore,  produce  acetic  acid.  On  the  contrary,  they  destroy  acetic 
acid,  produce  substances  of  disagreeable  tastes  and  odors  and  in  time 
may  putrefy  and  destroy  the  flavor  entirely. 

The  formation  of  the  "mother"  is  delayed  by  using  only  clear  wine 
and  by  avoiding  all  unnecessary  disturbances  of  the  film.  Before  it 
forms  in  any  considerable  amount  the  casks  or  vats  should  be  emptied, 
cleaned  and  started  afresh. 

Towards  the  end  of  the  acetic  fermentation  the  vinegar  bacteria  may 
become  harmful  in  another  way.  With  the  exhaustion  of  the  alcohol 
the  bacteria  are  obliged  to  attack  the  acetic  acid.  This  they  may  do, 
under  favoring  conditions,  so  vigorously  that  2  or  3  per  cent  of  acetic 
acid  may  disappear  in  a  few  weeks.  In  a  rapid  process  generator  this 
loss  may  occur  even  in  a  few  hours.  Finally,  the  vinegar  bacteria  may 
destroy  all  the  acetic  acid.  This  destruction  of  the  acetic  acid  does 
not  occur  until  the  alcoholic  contents  of  the  liquid  have  fallen  nearly 
to  1  per  cent  and  is  immediately  stopped  by  the  addition  of  a  new 
supply  of  wine.  It  is  prevented  by  drawing  off  the  vinegar  into  full, 
tightly  closed  casks  with  or  without  pasteurizing  as  soon  as  the  alcohol 
has  fallen  below  2  per  cent. 

Other  bacteria  may  produce  injurious  changes  at  the  beginning  before 
the  vinegar  bacteria  have  taken  possession  of  the  liquid.  Their  action 
is  prevented  by  a  preliminary  acetification  of  the  wine  by  means  of  an 
addition  of  10  per  cent  of  good  vinegar,  by  prompt  starting  of  the 
acetic  fermentation  by  means  of  a  strong  culture  of  vinegar  bacteria 
and,  when  necessary,  by  pasteurizing  the  wine  before  use. 

Injurious  bacteria  may  also  attack  the  vinegar  towards  the  end  of 
the  fermentation,  producing  putrid  odors.  These  are  prevented  by 
prompt  removal  to  the  storage  casks  as  soon  as  the  acetic  fermentation 
is  complete  and  by  pasteurizing  at  140°  F.  or  by  running  into  barrels 
in  which  a  stick  of  sulfur  has  been  burned. 

Mycoderma  vini  is  a  mold  growing  as  a  surface  film  like  the  vinegar 
bacteria.  It  attacks  the  alcohol,  breaking  it  up  into  water  and  car- 
bonic acid.     If  abundant  it  may  destroy  so  much  alcohol  as  to  make 


Bulletin  227]  GRAPE  VINEGAR.  359 

the  wine  unfit  for  vinegar.  It  is  most  troublesome  on  wines  rich  in 
albuminoids  and  extractive  matters,  especially  those  containing  a  rem- 
nant of  unfermented  sugar.  It  is  controlled  by  the  methods  recom- 
mended for  injurious  bacteria  and  is  less  liable  to  occur  if  the  wine 
is  well  fermented,  not  too  young,  and  clear  when  used. 

b.  Blackening.  Vinegars,  after  making,  will  often  turn  cloudy  by 
the  formation  of  a  fine  blackish  precipitate  on  exposure  to  the  air.  This 
may  be  due  to  the  same  oxydase  which  produces  the  same  trouble  in 
wine  and  is  cured  in  the  same  manner  by  a  light  sulfuring.  (See 
Bulletin  213.) 

It  may  also  be  caused  by  placing  the  vinegar  in  insufficiently  cleaned 
new  casks  from  which  it  extracts  tannic  substances  which  blacken  on 
contact  with  the  air.  Contact  with  iron  has  the  same  effect.  The 
acetic  acid  attacks  the  iron  and  forms  colorless  ferrous  salts  which 
change  to  dark-colored  ferric  salts  on  exposure  to  the  air. 

The  tannins  may  be  removed  by  treatment  with  gelatine  and  filter- 
ing through  animal  charcoal.  The  iron  salts  should  first  be  oxydized 
by  aeration  and  then  removed  by  fining  and  filtration.  The  addition 
of  a  minute  quantity  of  citric  acid  will  prevent  the  recurrence  of  the 
trouble  in  the  latter  case. 

c.  Animal  parasites.  One  of  the  commonest  and  most  troublesome 
diseases  of  vinegar  is  caused  by  a  nematode  worm,  the  "vinegar  eel." 
These  are  minute  wormlike  ani- 
mals which  can  be  seen  easily 
under  the  microscope  with  a 
slight  magnification  and  even 
with  the  unaided  eye  by  holding 
the  vinegar  before  a  bright  light 
in  a  small  glass. 

They  may  occur  in  the  vats 
and  generators  or  even  in  the 
finished  vinegar.  They  accumu- 
late most  numerously  around  the  edges  of  the  liquid  and  on  the  surface 
film.  They  interfere  with  the  acetification  by  destroying  this  film  and 
causing  it  to  sink.  When  numerous  they  are  not  only  disgusting  in 
themselves  but  are  the  cause  of  a  putrid  fermentation  that  may  com- 
pletely spoil  the  vinegar. 

They  are  easily  removed  from  the  finished  vinegar  by  filtration  fol- 
lowed by  pasteurization  or  sulfuring  and  fining.  In  the  acetifying 
vats  they  are  more  difficult  to  control.  An  infected  vat  or  cask  should 
be  emptied  as  soon  as  discovered,  washed  with  boiling  water  and  heavily 
sulfured.  The  source  of  the  first  infection  is  generally  river  or  sur- 
face water. 


360  UNIVERSITY  OF   CALIFORNIA EXPERIMENT   STATION. 

Unless  the  vinegar  factory  is  kept  clean,  vinegar  mites  may  appear 
in  large  numbers  and  become  troublesome.  They  are  minute  arachnids 
related  to  the  sugar  mites,  and  often  accumulate  in  moist  places  around 
the  vinegar  casks  or  generators.  They  may  even  enter  these,  and,  if 
numerous,  may  spoil  the  vinegar.  They  are  more  easily  controlled  than 
the  vinegar  eels  and  can  be  destroyed  with  hot  water.  They  may  be 
prevented  from  entering  the  casks  by  painting  a  ring  of  turpentine 
or  kerosene  oil  around  the  openings. 

Vinegar  flies  are  also  sometimes  troublesome,  especially  in  warm 
weather.  They  breed  around  the  openings  of  vinegar  containers  and 
wherever  they  can  find  vinegar  exposed  to  the  air.  If  numerous,  the 
maggots  they  produce  may  get  into  the  vinegar  and  much  deteriorate 
its  quality.  They  can  be  controlled  by  cleanliness  and  by  avoiding 
the  spilling  of  vinegar  and  the  leaking  of  casks.  It  is  sometimes 
necessary  to  screen  the  openings  of  casks  and  generators  with  mosquito 
nettings. 

XI.     OUTLINE  OF  THE  OPERATION  OF  VINEGAR  MAKING. 

A.  Gathering  the  grapes. 

The  better  the  grapes,  the  better  the  vinegar.  Grapes  suitable  for 
making  good  wine  will  make  good  vinegar.  The  grapes  should  be  ripe 
and  show  (in  California)  from  20°  B.  to  23°  B.  They  should  be 
gathered  and  handled  when  cold  or  cooled  by  exposure  to  the  night  air 
before  crushing. 

B.  Crushing  the  grapes. 

As  soon  as  possible  after  gathering,  the  grapes  should  be  crushed. 
The  crushing  should  be  thorough  but  the  seeds  should  not  be  broken. 
Any  of  the  ordinary  forms  of  roller  crushers  are  suitable.  Small  hand 
crushers  are  made,  suitable  for  small-scale  operations. 

C.  Extraction  of  the  juice. 

The  grapes  should  pass  from  the  crusher  into  an  open  vat  where 
fermentation  is  allowed  to  commence.  A  culture  of  pure  wine  yeast 
is  very  useful  in  insuring  a  prompt  and  good  fermentation.  After 
twenty-four  hours  of  fermentation  (shown  by  the  escape  of  gas  bub- 
bles) the  juice  should  be  separated  by  means  of  a  press.  The  pomace 
in  the  press  after  the  first  pressing  may  be  treated  with  water  and 
pressed  again  if  the  grapes  are  sweet  enough,  and  the  juice  thus  ob- 
tained may  be  mixed  with  the  rest.  No  more  water  should  be  used 
than  will  bring  the  mixed  juices  down  to  18°  or  20°  B.  A  home-made 
lever  press  is  efficient  and  satisfactory  where  small  quantities  of  grapes 
are  handled.  When  red  grapes  containing  a  large  amount  of  coloring 
matter  are  used,  it  may  be  necessary  to  press  out  the  juice  immediately 
after  crushing  and  without  the  preliminary  twenty-four  hours  of  fer- 


Bulletin  227]  GRAPE  VINEGAR.  361 

mentation.      The  yield  of  juice  will  in  this  case  be  from  10  to  20  per 
cent  less. 

D.  Alcoholic  fermentation. 

The  transformation  of  the  grape  juice  into  wine  may  take  place  in 
open  vats  of  any  convenient  size  up  to  1,000  gallons  or  in  the  casks 
which  are  to  be  used  later  for  the  acetic  fermentation.  In  the  latter 
case,  the  casks  should  be  well  cleaned  to  remove  all  vinegar. 

Fermentation  will  commence  spontaneously,  but  better  results  are 
obtained  by  using  pure  wine  yeast.  This  yeast  must  be  obtained  from 
a  reliable  source.  Bakers',  brewers'  or  distillers'  yeasts  do  not  give 
good  results  and  may  spoil  the  vinegar. 

The  maximum  temperature  of  the  fermenting  juice  should  not  ex- 
ceed 93°  F.  and  if  kept  below  86°  F.  the  results  are  better.  In  cold 
weather,  it  may  be  necessary  to  warm  the  fermenting  room.  In  hot 
weather,  the  temperature  requires  no  attention  where  very  small  casks 
or  vats  are  used.  With  large  casks  or  vats  artificial  cooling  is  some- 
times necessary. 

In  from  four  to  seven  days  all  sugar  perceptible  to  the  taste  should 
have  disappeared  and  the  juice  has  then  become  wine. 

E.  Treatment  of  the  wine. 

As  soon  as  fermentation  is  over  the  wine  should  be  placed  in  casks 
which  should  be  filled  completely  and  bunged  up  tight  as  soon  as  gas 
has  ceased  to  be  given  off.  At  the  end  of  two  or  three  weeks  most  of 
the  yeast  and  other  solid  matter  will  have  settled  into  the  lees.  The 
clear  wine  should  then  be  drawn  off  the  sediment.  It  may  be  drawn 
directly  into  the  vinegar  casks  and  the  acetic  fermentation  started 
immediately.  If  this  is  not  convenient,  it  may  be  drawn  into  clean 
storage  casks  and  kept  for  as  long  as  desired.  These  storage  casks 
should  be  kept  quite  full  and  the  wine  racked  from  the  sediment  which 
will  form,  every  two  or  three  months.  At  any  time  after  it  is  clear, 
the  wine  may  be  turned  into  vinegar.  The  vinegar  casks  may  be  used 
for  storage  by  closing  the  air  vents  with  wooden  bungs. 

F.  Acetic  fermentation. 

Before  placing  in  the  vinegar  casks  or  generators,  the  wine  should 
be  free  from  all  gross  sediment.  If  very  cloudy,  it  should  be  filtered. 
If  too  red,  it  is  best  decolorized  before  acetification.  The  best  results 
are  obtained  by  pasteurizing  the  wine  before  placing  in  the  vinegar 
casks. 

Enough  good  vinegar  should  be  added  to  the  wine  to  increase  its 
volatile  acidity  to  at  least  1  per  cent.  One  gallon  of  strong  vinegar 
to  nine  gallons  of  wine  will  suffice.  In  replenishing  the  wine  in  a  vine- 
gar cask  in  operation,  the  vinegar  remaining  in  the  cask  is  sufficient. 
The  vinegar  added  (if  not  pasteurized)  supplies  the  necessary  bacteria 
which  are  the  cause  of  acetincation. 


362  UNIVERSITY   OF   CALIFORNIA EXPERIMENT  STATION. 

The  temperature  should  be  fairly  uniform  and  if  possible  between 
65°  F.  and  75°  F.  Below  65°  F.  the  process  is  unnecessarily  slow; 
above  75°  F.  the  quality  suffers  and  the  loss  from  evaporation  is  ex- 
cessive. With  rapid  process  generators,  higher  temperatures  may  be 
used,  about  86°  F.  being  the  most  favorable.  In  the  slow  process,  the 
temperature  of  the  fermenting  vinegar  will  be  that  of  the  room.  In 
the  rapid  process  it  will  be  20°  to  30°  F.  higher. 

There  must  be  free  access  of  air  to  the  surface  of  the  liquid  in  the 
casks,  but  vinegar  flies  and  dust  must  be  excluded.  After  from  one  to 
three  months  the  acetic  fermentation  should  be  complete  in  the  slow 
processes,  though  this  time  may  be  much  prolonged  if  the  temperature 
of  the  vinegar  room  is  too  low. 
G-.     After-treatment  and  aging. 

The  end  of  the  acetic  fermentation  is  determined  by  tasting  and 
by  measuring  the  amount  of  acetic  acid  present  by  means  of  an  acido- 
meter.  Tests  should  be  made  at  intervals  in  order  to  follow  the 
progress  of  the  fermentation.  When  the  acidometer  shows  that  the 
vinegar  has  approximately  the  maximum  acidity  to  be  expected  from 
the  sugar  contents  of  the  original  must  or  from  the  alcoholic  percentage 
of  the  wine,  the  process  is  finished.  If  a  second  test  several  days  or 
weeks  after  the  first  shows  a  diminution  of  acidity,  the  process  has  gone 
too  far.  In  either  of  these  cases  the  vinegar  should  be  taken  out  of  the 
fermenting  casks  and  all  bacterial  action  stopped.  This  is  done  by 
placing  it  in  completely-filled,  tightly-bunged  casks  stored  in  a  cool 
cellar.  Pasteurization  of  the  vinegar  at  140°  F.  before  placing  in  the 
storage  casks  is  to  be  recommended. 

In  storage  casks  the  vinegar  requires  no  treatment  except  filling  up 
and,  if  it  is  kept  more  than  a  few  months,  one  or  two  rackings.  The 
rackings  should  be  done  with  as  little  exposure  to  the  air  as  is  prac- 
ticable. 

H.     Preparation  for  sale. 

The  vinegar  should  be  perfectly  bright  and  free  from  bacteria  when 
sold.  This  is  accomplished  by  fining  or  filtering  and  when  bottled  by 
pasteurizing  after  bottling. 

XII.     TESTS   OF  USE  TO   VINEGAR   MAKERS. 

The  vinegar  manufacturer  should  have  some  reliable  means  of  de- 
termining the  amount  of  sugar  in  the  grapes  and  of  alcohol  in  the  wine. 
He  should  also  be  able  to  test  his  vinegar  during  the  process  of  acetifi- 
cation  in  order  to  determine  the  proper  time  for  stopping  the  process. 

Note. — Acetic  acid  attacks  most  metals  very  readily,  forming  poisonous  salts. 
Pure  tin  and  certain  alloys  consisting  principally  of  tin  are  not  attacked.  All  filters, 
presses,  buckets,  etc.,  used  for  handling  vinegar  should  be  of  wood  or  earthenware. 
The  hoops  of  buckets,  tubs,  or  casks,  and  all  metallic  surfaces  in  the  factory,  should 
be  well  painted  or  varnished  to  protect  them  from  the  vinegar  fumes  which  would 
otherwise  quickly   corrode   them. 


Bulletin  227] 


GRAPE  VINEGAR. 


363 


5? 


N^ 


a.  Sugar.  The  ordinary  Balling  saccharometer  commonly  used  by 
wine  makers  is  equally  suitable  for  the  vinegar  maker.  It  consists  of 
a  hydrometer  or  spindle  (s)  with  a  long  neck  graduated  in  degrees. 

In  using,  it  is  floated  in  the  solution  (grape  juice)  to  be  tested  con- 
tained in  a  long  narrow  glass  cylinder.  The  more  deeply  it  sinks,  the 
less  sugar  the  solution  contains.  By  noting  the  degree 
which  corresponds  to  the  surface  of  the  liquid  we  have 
a  sufficiently  accurate  measure  of  the  sugar  contents. 
This  degree  represents  the  percentage  of  sugar  by 
weight  in  a  pure  sugar  solution  of  the  same  specific 
gravity  as  the  juice.  As  this  juice  contains  other  sub- 
stances beside  sugar,  the  real  sugar  contents  will  be 
from  .5  per  cent  to  2.5  per  cent  less  than  the  indicated 
Balling  per  cent  or  degree.  These  non-saccharine  sub- 
stances will  vary  in  different  grapes,  so  that  the 
Balling  degree  gives  us  only  an  approximation  of  the 
amount  of  sugar  present.  This  is  quite  close  enough 
for  the  purposes  of  the  vinegar  maker,  however,  and 
by  reference  to  Table  VI  on  page  350  he  can  determine 
very  closely  how  much  alcohol  and  how  much  acetic 
acid  he  should  obtain  by  fermentation.  This  will 
enable  him  to  make  the  calculations  necessary  in  blend- 
ing juices  of  various  degrees  of  sweetness  and  in 
adding  water  to  juices  containing  too  much  sugar. 

The  accuracy  of  the  test  depends  on  the  care  with 
which  it  is  made.  The  juice  should  be  quite  fluid,  that 
is,  it  should  not  contain  enough  floating  solid  matter 
to  make  it  thick  or  slimy,  otherwise  the  resting  point 
of  the  saccharometer  will  be  uncertain. 

The  test  should  be  made  before  the  commencement 
of  fermentation,  otherwise  the  alcohol  formed  and  the 
bubbles  of  carbonic  acid  gas  coming  off  may  make  the  reading  com- 
pletely unreliable. 

The  saccharometer  should  be  cleaned  and  dried  each  time  before 
using.  When  greasy  it  should  be  cleaned  with  a  little  alcohol  or  bicar- 
bonate of  soda  and  warm  water.  It  should  be  handled  with  clean  dry 
hands  or  a  clean  cloth.  Any  grease  or  juice  or  water  on  the  stem  may 
notably  change  the  result. 

The  reading  should  be  made  at  the  true  level  of  the  liquid  as  indi- 
cated in  Fig.  6.  By  capillarity,  the  liquid  in  contact  with  the  glass 
rises  more  or  less  above  the  true  surface,  forming  what  is  known  as 
the  meniscus  (m.)      The  bottom  of  this  meniscus  is  the  true  surface. 

The  specific  gravity  of  the  juice  varies  with  the  temperature.  For 
this  reason  the  juice  must  be  brought  to  the  standard  temperature  for 


Fig.    6. 

Method    of    reading 

a  hydrometer. 


364 


UNIVERSITY  OF   CALIFORNIA EXPERIMENT   STATION. 


which  the  saccharometer  is  adjusted  (usually  60°  F.)  or  a  temperature 
correction  made.  This  correction  is  very  nearly  .1  per  cent  for  every 
3  degrees  Fahrenheit  above  or  below  the  standard.  If  the  temperature 
is  higher,  this  correction  must  be  added,  if  lower,  subtracted. 


Fig.  7. — Still  for  Alcohol  Tests. 

b.  Alcohol.  "When  the  fermentation  of  the  must  is  complete  the 
sugar  has  disappeared  and  has  been  replaced  by  alcohol  which  remains 
in  the  liquid  and  by  carbonic  acid  gas  which  passes  into  the  atmosphere. 
The  end  of  the  fermentation  is  determined  accurately  enough  for  our 
purpose  by  taste.  When  the  wine  is  dry,  that  is,  when  no  sweet  taste 
can  be  perceived,  the  sugar  has  practically  all  disappeared.  The  wine 
should  then  show  an  amount  of  alcohol  corresponding  to  the  original 
Balling  degree  as  shown  in  Table  VI  on  page  350. 

The  actual  amount  of  alcohol  can  be  determined  by  means  of  a  small 
still  (Fig.  7).  This  still  consists  of  a  small  glass  or  copper  vessel  in 
which  the  wine  is  boiled.  The  vapors  given  off  are  condensed  by  pass- 
ing from  the  boiler,  through  a  spiral  tube  immersed  in  cool  water,  and 
the  liquid  runs  into  a  measuring  flask. 

To  make  a  determination  of  alcohol,  100  cubic  centimeters  of  the 
wine  are  measured  exactly  in  the  measuring  flask.  The  liquid  is  then 
poured  into  a  beaker  and  its  acidity  neutralized  by  adding  a  solution 
of  caustic  soda  or  potash.  The  point  of  neutralization  is  determined 
by  means  of  a  piece  of  red  litmus  paper.  The  neutralized  wine  is  then 
poured  into  the  boiler  together  with  a  little  pure  water  with  which 
the  flask  and  beaker  have  been  rinsed.  The  wine  should  be  as  near 
60°  F.  as  practicable  when  measured. 

The  boiler  is  now  conected  with  the  condenser,  and  the  measuring 


Bulletin  227] 


GRAPE  VINEGAR. 


365 


flask,  after  careful  and  thorough  rinsing,  is  placed  to  catch  the  dis- 
tillate. All  connections  must  be  perfectly  tight.  The  boiler  should 
be  about  one  third  full. 

The  heating  should  be  gentle  at  first  and  more  rapid  later  but  any 
spurting  of  liquid  into  the  condenser  must  be  avoided.  The  water  in 
the  condenser  should  never  exceed  70°  F.  When  half  of  the  liquid 
has  distilled  over  the  process  may  be  stopped.  After  cooling  to  60°  F. 
water  is  added  to  the  distillate  in  the  measuring  flask  until  the  original 
volume  is  reached.  The  liquid  is  then  poured  into  the  cylinder  and 
the  degree  of  alcohol  read  off  by  means  of  the  floating  alcoholimeter. 

The  same  care  is  necessary  in  reading  the  alcoholimeter  as  already 
described  for  the  Balling  saccharometer.  (See  page  363.)  The  tem- 
perature of  the  liquid  should  be  as  near  60°  F.  as  possible,  and  any 
variation  from  this  temperature  allowed  for  by  consulting  the  table 
of  temperature  corrections  furnished  with  the  still. 

In  determining  the  alcohol  in  vinegar,  all  the  acidity  must  be  neu- 
tralized before  distillation.  For  this  purpose  the  caustic  soda  solution 
must  be  very  concentrated  or  the  volume  of  the  liquid  necessary  to  add 
will  be  too  great  for  the  boiler.  The  1  or  2  per  cent  of  alcohol  which 
it  is  desirable  to  leave  at  the  end  of  the  acetic  fermentation  can  be  deter- 
mined with  sufficient  accuracy  by  this  means. 

c.  Acetic  acid.  To  determine  exactly  the  strength  of  the  vinegar, 
that  is  the  exact  amount  of  acetic  acid  it  contains,  requires  time,  skill 

and  somewhat  complicated  appa- 
ratus. To  determine  its  strength 
with  sufficient  accuracy  for  manu- 
facturing and  commercial  purposes 
is  very  simply  done  by  means  of  some 
of  the  forms  of  ' '  vinegar  testers. ' ' 

In  the  form  shown  in  Fig.  8  the 
acetic  acid  is  determined  by  the  vol- 
ume of  gas  given  off  by  bicarbonate 
of  soda  when  treated  with  a  meas- 
ured volume  of  vinegar. 

The  requisite  volume  of  vinegar  is 
measured  in  the  small  glass  tube  A 
and  poured  into  the  bottle  B.  A 
sufficient  amount  of  bicarbonate  is 
then  taken  with  the  spoon  E  and 
introduced  carefully  into  the  bottle. 
As  soon  as  the  bottle  is  tightly  closed 
with  the  cork  the  bicarbonate  is 
shaken  gradually  into  the  vinegar 
and  immediately  carbonic  acid  gas 
commences  to  be  given  off.  This  gas, 
fig.  8.— vinegar  Tester.  passing    through    the    rubber    tube, 

forces  the  water  in  the  bottle  D  to  rise  in  the  large  glass  tube  C.     The 


366 


UNIVERSITY   OF   CALIFORNIA EXPERIMENT   STATION. 


stronger  the  vinegar  the  more  gas  will  be  given  off  and  the  higher 
the  water  will  rise  in  the  tube  C.  This  tube  is  marked  with  numbered 
lines.  By  reading  the  number  of  the  line  nearest  the  level  reached  by 
the  water  and  adding  the  estimated  height  above  or  below  this  line,  the 
strength  of  the  vinegar  is  obtained  directly  in  per  cent.  If  the  vinegar 
is  made  from  wine  .5  per  cent  must  be  deducted  from  the  observed  read- 
ing to  allow  for  the  tartaric  acid  of  the  wine. 

To  insure  sufficient  accuracy  with  these  instruments  certain  precau- 
tions are  necessary.  The  bicarbonate  of  soda  sold  for  cooking  pur- 
poses is  sufficiently  pure.  In  placing  it  in  the  bottle  care  should  be 
taken  that  none  get  into  the  vinegar  until  the  bottle  is  securely  corked. 
There  must  be  no  leak  in  the  apparatus.  This  is  determined  by  allow- 
ing the  column  of  water  to  remain  for  a  few  minutes  in  the  cylinder 
after  making  a  determination.  If  the  column  does  not  fall  in  this 
time  there  is  no  leak  of  importance. 

The  instruments  are  adjusted  for  water  of  ordinary  temperature. 
If  the  water  is  either  very  cold  or  very  warm  the  results  are  inaccurate. 
The  following  table  shows  some  of  the  variations  due  to  the  use  of 
too  warm  water. 

Table  VII. 
Results  with  vinegar  tester  compared  with  accurate  analyses. 


Vinegar. 


Reading  of  vinegar  tester,  at — 


1 

2 
3 

1 

5 
6 


3.02 

2.9 

3.2 

4.55 

4.4 

4.6 

6.50 

6.4 

6.6 

7.04 

7.0 

7.4 

8.49 

8.5 

8.7 

10.15 

10.1 

10.7 

3.3 

4.7 
6.9 
7.7 
9.1 
11.2 


No  temperature  correction  is  possible  as  the  variations  are  irregular. 
At  65°  F.  as  shown  in  the  table  the  determinations  agree  very  closely 
with  the  results  of  more  accurate  tests.  There  are  other  sources  of 
error  such  as  the  atmospheric  pressure,  the  pressure  of  the  column  of 
water  and  the  absorption  of  gas  by  the  water,  but  they  are  none  of  them 
large  enough  to  be  of  any  significance  to  the  vinegar  maker. 


STATION    PUBLICATIONS    AVAILABLE    FOR    DISTRIBUTION. 


REPORTS. 

1896.  Report  of  the  Viticultural  Work  during  the  seasons  1887-93,  with  data  regard- 

ing the  Vintages  of  1894-95. 

1897.  Resistant  Vines,    their   Selection,   Adoption,    and   Grafting.      Appendix   to   Viti- 

cultural Report  for   1896. 

1902.  Report  of  the  Agricultural  Experiment  Station  for  1898-1901. 

1903.  Report  of  the  Agricultural  Experiment  Station  for  1901-03. 

1904.  Twenty-second  Report  of  the  Agricultural  Experiment  Station  for  1903-04. 


BULLETINS. 


Reprint. 
No.    128. 

133. 

147. 

149. 
162. 

164. 

165. 

167. 

168. 

169. 

170. 
171. 

174. 
176. 

177. 

178. 
179. 

181. 
182. 


183. 
184. 

185. 

186. 

187. 

188. 

189. 

190. 
191. 
192. 

193. 


Endurance  of  Drought  in  Soils  of 
the  Arid  Regions. 

Nature,  Value,  and  Utilization  of 
Alkali  Lands,  and  Tolerance  of 
Alkali.  (Revised  and  Reprint, 
1905.) 

Tolerance  of  Alkali  by  Various 
Cultures. 

Culture  Work  of  the  Sub-sta- 
tions. 

California  Sugar  Industry. 

Commercial  Fertilizers.  (Dec.  1, 
1904.) 

Poultry  Feeding  and  Proprietary 
Foods. 

Asparagus  and  Asparagus  Rust 
in   California. 

Manufacture  of  Dry  Wines  in 
Hot  Countries. 

Observations  on  Some  Vine  Dis- 
eases in  Sonoma  County. 

Tolerance  of  the  Sugar  Beet  for 
Alkali. 

Studies  in  Grasshopper  Control. 

Commercial  Fertilizers.  (June 
30,   1905.) 

A  New  Wine-cooling  Machine. 

Sugar  Beets  in  the  San  Joaquin 
Valley. 

A  New  Method  of  Making  Dry 
Red  Wine. 

Mosquito   Control. 

Commercial  Fertilizers.  (June, 
1906.) 

The  Selection  of  Seed-Wheat. 

Analyses  of  Paris  Green  and 
Lead  Arsenic.  Proposed  in- 
secticide Law. 

The  California  Tussock-moth. 

Report  of  the  Plant  Pathologist 
to  July  1,   1906. 

Report    of    Progress    in    Cereal 
Investigations. 

The  Oidium  of  the  Vine. 

Commercial  Fertilizers.  (Janu- 
ary,  1907.) 

Lining  of  Ditches  and  Reservoirs 
to  Prevent  Seepage  and  Losses. 

Commercial  Fertilizers.  (June, 
1907.) 

The  Brown  Rot  of  the  Lemon. 

California  Peach  Blight. 

Insects  Injurious  to  the  Vine  in 
California. 

The  Best  Wine  Grapes  for  Cali- 
fornia ;  Pruning  Young  Vines ; 
Pruning  the  Sultanina. 


No.  194. 

195. 
197. 


198. 
199. 
200. 


201. 

202. 

203. 

204. 

205. 

206. 

207. 

208. 
209. 
210. 

211. 

212. 
213. 
214. 

215. 

216. 

217. 
218. 
219. 

220. 

221. 

222. 
223. 
224. 

225. 

226. 


Commercial  Fertilizers.  (Dec, 
1907.) 

The  California  Grape  Root- 
worm. 

Grape  Culture  in  California ; 
Improved  Methods  of  Wine- 
making  ;  Yeast  from  California 
Grapes. 

The  Grape  Leaf-Hopper. 

Bovine  Tuberculosis. 

Gum  Diseases  of  Citrus  Trees  in 
California. 

Commercial  Fertilizers.  (June, 
1908.) 

Commercial  Fertilizers.  (Decem- 
ber, 1908.) 

Report  of  the  Plant  Pathologist 
to  July  1,   1909. 

The  Dairy  Cow's  Record  and  the 
Stable. 

Commercial  Fertilizers.  (Decem- 
ber,   1909.) 

Commercial  Fertilizers.  (June, 
1910.) 

The  Control  of  the  Argentine 
Ant. 

The  Late  Blight  of  Celery. 

The  Cream  Supply. 

Imperial  Valley  Settlers'  Crop 
Manual. 

How  to  Increase  the  Yield  of 
Wheat   in   California. 

California  White  Wheats. 

The   Principles   of  Wine-making. 

Citrus  Fruit  Insects. 

The  Housefly  in  its  Relation  to 
Public  Health. 

A  Progress  Report  upon  Soil  and 
Climatic  Factors  influencing  the 
Composition  of  Wheat. 

Honey  Plants  of  California. 

California  Plant  Diseases. 

Report  of  Live  Stock  Conditions 
in  Imperial  County,   California. 

Fumigation  Studies  No.  5  Dosage 
Tables. 

Commercial  Fertilizers.  (Oct., 
1911.) 

The  Red  or  Orange  Scale. 

The  Black  Scale. 

The  Production  of  the  Lima 
Bean.. 

Tolerance  of  Eucalyptus  for  Al- 
kali. 

The  Purple  Scale. 


CIRCULARS. 


No.     1.  Texas  Fever. 

7.  Remedies  for   Insects. 
9.  Asparagus  Rust. 

10.  Reading  Course  in  Economic  En- 

tomology. 

11.  Fumigation  Practice. 

12.  Silk  Culture. 

15.  Recent    Problems    in    Agriculture. 
What  a  University  Farm  is  For. 

19.  Disinfection  of  Stables. 

29.   Preliminary    Announcement    Con- 
cerning Instruction   in   Practical 
Agriculture  upon  the  University 
Farm,  Davis,  Cal. 
White  Fly  in  California. 


30. 

32.   White  Fly  Eradication. 

33. 


86. 


39. 


Cane 


Packing    Prunes    in    Cans. 

Sugar  vs.  Beet  Sugar. 
Analyses    of    Fertilizers    for    Con- 
sumers. 
Instruction    in    Practical    Agricul- 
ture at  the  University  Farm. 
46.   Suggestions   for   Garden   Work   in 

California   Schools. 
50.   Fumigation   Scheduling. 


No.  52.  Information  for  Students  Concern- 
ing the  College  of  Agriculture. 

Some  Creamery  Problems  and 
Tests. 

Farmers'  Institutes  and  Univer- 
sity   Extension     in    Agriculture. 

Experiments  with  Plants  and  Soils 
in  Laboratory,  Garden,  and 
Field. 

60.  Butter  Scoring  Contest,   1910. 

61.  University  Farm  School. 

62.  The  School  Garden  in  the  Course 
of  Study. 

How  to  Make  an  Observation  Bee 

Hive. 
Announcement  of  Farmers'   Short 

Courses  for  1911. 
The  California  Insecticide  Law. 
Insecticides  and  Insect  Control. 
Development  of  Secondary  School 

Agriculture  in  California. 
The    Extermination    of    Morning- 

Glory. 
Observation  of  the  Status  of  Corn 

Growing  in  California. 


54. 


55. 


58. 


63. 

64. 

65. 
66. 
67. 

69. 

70. 


